True enough. However if you are going to use KindleGen to make the mobi file then you might as well start with ePub these days. KindleGen will look at the file and map what it can while ignoring the rest and make a reasonable mobi file. KindleGen creates both mobi formatted and KF8 formatted file (contains both). This can then be separated by Amazon to deliver the appropriate file to users. If you are making something for yourself then there are tools to take the two halves apart to diminish the file size but it will work even if you don't.